The lipoxygenase (LOX) family of enzymes has well established roles in inflammation (5-LOX and the leukotrienes), and yet-to-be fully defined roles in cell differentiation and proliferation. The recent finding of a human genetic defect in two LOX enzymes associated with an inherited form of ichthyosis presents an opportunity to connect the functioning of these enzymes with a role in epidermal differentiation. The genetics identifies both 12R-LOX and eLOX3 (epidermal lipoxygenase-3) as defective in the families studied, and by implication, as playing a critical and important role in all normal individuals. We recently found a plausible biochemical explanation for the genetics: the two lipoxygenases, 12R-LOX and eLOX3 act in tandem to convert arachidonic acid to a specific epoxyalcohol metabolite. Here we propose to investigate the role of this LOX pathway, pursuing the overall hypothesis that it has a vital function in keratinocyte differentiation, by characterizing substrates, intermediates, and products of the intertwined LOX activities, and the ability of these metabolites to activate or modulate the differentiation process in keratinocytes. The Specific Aims are: To characterize the enzymology and pathways of metabolism involving 12R-LOX and eLOX3; To determine the functional relationships between 12R-LOX and eLOX3 by analyses of their expression, activities and localization in cells and tissues; To determine the biological activities of the 12R-LOX/eLOX3-derived products The failure of keratinocytes to correctly differentiate is a hallmark of severe skin diseases like psoriasis or ichthyosis. The results of this study will help characterize a model for LOX enzyme activity in controlling cell differentiation in a well-defined human context of disease, as well as uncovering the activities of a new class of agents, epoxyalcohols and their derivatives, with the potential for future therapeutic interventions.